Electrical heating devices



Dec. 17, 1963 G. v. WOODLING 3,114,319

ELECTRICAL HEATING DEVICES Original Filed Oct. 21, 1948 4 Sheets-Sluget1 INVENT R.

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' ms INSUL AT/ON I L /44/N$ULA T/0N /45 45 17, 1963 G. v. WOODLING3,114,819

ELECTRICAL HEATING DEVICES Original Filed Oct. 21, 1948 4 Sheets-Sheet 297 ALTER/VA T/NG I CURRENT SOURCE 76 /PUT AL TER/VA T/NG CURRENT lSOURCE I E (VIN VEN TOR. BY 5 Dec. 17, 196.3 G. v. WOODLING 3,114,819

ELECTRICAL HEATING DEVICES Original Filed Oct. 21, 1948 4 Sheets-Sheet 3AL TERNA TING CURRENT sou/ace AL TERA/A77 CURRENT l SOURCE I AL TEE/VATING C URREN 7' WWENTOR.

United States Patent 3,114,819 ELECTRICAL HEATING DEVICES George V.Woodling, 815 Union Commerce Bldg, Cleveland, Ohio Application Sept. 21,1%3, Ser. No. 3%1,310, now Patent No. 3,007,026, dated Oct. 31, 1961,which is a division of application Scr. No. 55,791, Get. 21, 1948, nowPatentNo. 2,673,917, dated Mar. 30, W54. Divided and this applicationDec. 27, 1960, Ser. No. 78,545 4 Claims. (Cl. 21*}20) The inventionrelates in general to electrical heating appliances and moreparticularly to household heating appliances which may be controlled bya controllable space discharge device and which utilizes a metallic filmimpedance for the heating element.

This application claims subject matter disclosed in my Patents No.2,673,917 and No. 3,007,026, the latter being a division of the former,and applicant relies upon the filing dates of the applications fromwhich these patents matured since this case is a division of applicationNo. 381,310 now Patent No. 3,007,026.

An obj ect of the inventionv is to provide a household electricfiat-iron with rectified alternating current energy from a rectifiercontrolled by a temperature responsive impedance in heat exchangerelationship with the fiatiron.

Another object of the invention is to provide a temperature responsiveimpedance in heat exchange relationship with a household electricalheating appliance to effect a bridge circuit and thus control acontrollable rectifier supplying energy to the appliance, and further toplace such impedance in circuit relation with the energy output of therectifier.

Another object of the invention is to provide a household electricheating appliance wherein the heating element is a metallic resistorfilm deposited on a dielectric coating which is in turn supported by ametal carrier.

A still further object of the invention is to provide a householdelectric appliance adapted to be heated by a metallic film heatingelement with such film deposited on a dielectric coating and wherein themetallic film is supplied withelectrical energy from a controllablerectifier, and a control circuit has a temperature responsive impedancein heat'exchange relationship with the heating element to control thecontrollable rectifier.

A still further object of the invention is to provide a householdelectric appliance adapted to be heated by a heating element suppliedwith electrical energy from a controllable rectifier, and a controlcircuit has a temperature responsive element in heat exchangerelationship with the heating element to control the controllablerectifier, and wherein either or both of the elements may be a metallicfilm.

Other object and a fuller understanding of this invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a plan view of a metallic carrier supporting a dielectriccoating which in turn supports a metallic film impedance used as aheating element;

FIGURE 2 is a cross-sectional view of FIGURE 1 showing the metallic filmin exaggerated thickness;

FIGURE 3 is a sectional elevational view of a fiatiron incorporating ametallic film heating element;

FIGURE 4 is a sectional plan view taken on the line 4d of FIGURE 3;

FIGURE 5 is a partial sectional elevational view of a modified form offiatiron incorporating a metallic film impedance;

FIGURE 6 is a circuit diagram of a controllable supply circuit for theheating element;

FIGURE 7 is a vector diagram of the voltages obtainable from the circuitof FIGURE 6;

FIGURE 8 is another controllable supply circuit for the heating element;

FIGURE 9 is a further modification of a controllable supply circuit;

FIGURES 10 and 11 are still further modifications of a controllablesupply circuit;

FIGURE 12 is a circuit diagram of a controllable energization circuitwhich incorporates a portion of the heating element in the phase shiftbridge control circuit;

FIGURE 13 is a vector diagram of the vectors obtainable from the circuitof FIGURE 12;

FIGURE 14 is a modification of the circuit of FIG- URE 12:

FIGURE 15 is a vector diagram of the vectors obtainable from the circuitof FIGURE 14;

FIGURE 16 is a controllable energization circuit for a heating appliancehaving a control impedance in the heating appliance; and

FIGURE 17 is a vector diagram of the vectors obtainable from the circuitof FIGURE 16.

FlGURES 1 and 2 illustrate one form of the invention wherein a metalliccarrier 21 has recessed portions 22 and the entire upper surface 23 iscovered with a dielectric or vitreous enamel coating 24. Terminal plates25 are adapted to be attached or imbedded in the dielectric coating 24at the recessed portions 22 and remain fixedly in place. A metallic filmimpedance 26 is adapted to be deposited in any well-known manner uponthe dielectric coating 24 and terminal plates 25. A second dielectriccoating 27 is adapted to cover the metallic film impedance 26 and toextend down over the sides to the metallic carrier 21 to act aselectrical insulation and mechanical protection to the metallic filmimpedance 26. The manner of applying the metallic film impedance and themanner of applying and type of dielectric coating does not form part ofthe invention. The upper surface 28 of the second dielectric coating 27is preferably made of a smooth surface so that the entire heating unitmay be more satisfactorily utilized; for instance, the heating unitmight be used as a hot plate or other appliance wherein a smooth workingsurface would be desirable. Electrical connection to the metallic filmimpedance is made by the terminal plates 25 since these terminal platesare directly in contact with the metallic film impedance 26. Terminalwires 77 may be attached to the terminal plates by any wellknown meanssuch as soldering or brazing, and in the FIGURES 1 and 2 have been shownas being attached to the underside ot the terminal plates 25 and gainingaccess to such terminal plates through holes 78 in the metallic carrier21.

The FIGURE 2 shows the layers of dielectric coating and metallic film incross section, and it is to be understood that this cross-sectional viewis considerably exaggerated, especially as to the thickness of themetallic film impedance.

The FIGURES 3 and 4 show a metallic film impedance as applied to ahousehold heating appliance shown as an electric fiatiron 29. Thefiatiron 29 includes a metal soleplate 30 having a Working surface 31and an opposite surface 32. A dielectric coating such as a vitreousenamel coating 33 is adapted to cover the opposite surface 32 of themetal soleplate 30 to act as an insulator. Such dielectric or vitreousenamel coating 33 may be applied in liquid state and may be such coatingthat is fired to a hard, glossy surface covering the opposite surface32. A metallic film impedance 34 may be deposited on the dielectriccoating 33 as the heating element of the fiatiron 29. A seconddielectric coating 35 covers the metallic film impedance 34 to providephysical protection to the metallic film impedance 34 and to act as anelectrical and heat insulator. The heating element may be made insubstantially the same manner as is used in the trade in mailing thinmetallic film resistors. The vitreous enamel physically protects thethin metal resistor film from abrasion and moisture. With this type ofconstruction, the entire electrical appliance may be washed withoutdamage to the heating element and thus is rendered sanitary. Theresistor film may have Zero, negative or positive temperaturecoefiicient. Metal terminal plates 36 and 37 have been shown at the toeand heel portions of the flatiron 29 to provide electrical connection tothe metallic film impedance 34. These metal terminal plates 36 and 37have been shown as being placed on the first dielectric coating 33whereupon the metallic film impedance 34 is deposited on these metalterminal plates as well as on the first dielectric coating 33. The metalterminal plates 36 and 37 provide suflicient thickness of metal toprovide electrical connection to the wires 38 and 3% such as bysoldering or brazing at the terminals 44). The Wires 38 and 39 may bejoined into a cable 41 having a conventional male electrical plug 42.

A solid heat insulating cover 43 may cover the entire opposite surface32 of the soleplate 36. This cover 4-3 may be of any solid insulatorsuch as a plastic or any other well-known insulating substance. Thecover 43 has a handle portion 4-4. The cover 43 is adapted to befastened to the soleplate 36 by cap screws 45 which threadedly engageprojecting lugs 46 on the opposite surface 32 of the soleplate 3t) andpreferably the cap screws 45 are recessed in the cover 43 as at 67.

The flatiron shown in FIGURES 3 and 4 is an improved form of flatironsince the use of the metallic film impedance 34 permits lightweightconstruction of the fiatiron, and also permits a minimum thicknessbetween the working surface 31 and the upper surface 4% of the cover 43.

The FIGURE shows a portion of a flatiron 149 that differs in someparticulars from the fiatiron 2? of FIG- URES 3 and 4. A plate 141 maybe made of metal as is the usual custom and has a recess 142 to receivea terminal plate 143. Between the terminal plate 143 and the recess 14.2is a dielectric coating 144 which completely covers the lower surface ofthe plate 141. A metallic film impedance 145 is deposited on thedielectric coating 14-4 and is, hence, in electrical contact with theterminal plate 143. A second dielectric coating 146 is deposited on themetallic film impedance 145 and also preferably covers the toe portion147 of the plate 141 as well as the entire side edges of the plate 141,for electrical insulation and for mechanical protection to the metallicfilm impedance 1 By providing a fiat surface to the first dielectriccoating 144 the metallic film impedance 145 and the second dielectriccoating 146 will also have a flat surface to thus provide a smoothworking surface for the fiatiron 140. Such flat surface may be obtainedby grinding or other suitable method to eliminate any unevennessv A hole143 is provided in the plate 141 so that a terminal wire 149 may gainaccess to the terminal plate 143 and be electrically connected theretoin any suitable manner.

The circuit of FIGURE 6 shows an energization circuit 53 which may becontrolled in electrical output for energizing the heating element of ahousehold electrical appliance. A household heating appliance 51 hasbeen shown in dotted lines to indicate a flatiron having a heat ingelement 52. The energization circuit 53 is preferably housed in aseparate housing as indicated by the dashed line 54. The energizationcircuit 53 includes generally a transformer 55 having a primary 56energizable from an alternating current source 57 through the switch 53.A secondary 5% of the transformer 55 energizes the anodes 60 of spacedischarge devices 61. These space discharge devices have been shown asgaseous discharge tubes having a control element such as control grids62. The space discharge devices have been shown as constituting a fullwave rectifier system having a rectified alternating curl rent outputdeliverable across the output terminals 63 and 6d. The rectified outputof the rectifiers 61 is delivered to the heating element 52 forenergization thereof.

The energization circuit 53 also includes a control circuit 65 having aphase shift bridge 66 energized from a transformer winding 67. The phaseshift bridge 66 has four arms with the first arm 75 including a manuallyvariable resistance 68 and acapacitive element 69. The second armincludes an impedance 70 shown as a resistance. The third arm is atemperature responsive impedance 71 that is shown in heat exchangerelationship with the heating element 52. In this case, the temperatureresponsive impedance 71 is shown as being enclosed within the confinesof the flatiron 51. The fourth arm of the bridge 66 includes anotherimpedance shown as a resistance 72. The output of the bridge 66 atterminals 74 and 76 is supplied to a grid transformer 73 to variablyshift the phase of the grid-cathode voltage relative to theanode-cathode voltage of the space discharge devices 61.

The vector diagram of FIGURE 7 may be referred to as an aid inunderstanding the operation of the circuit of FIGURE 6. in all thefollowing vector diagrams the voltage vectors will be given a referencecharacter corresponding to the reference character of the voltage sourceor impedance across which the voltage drop occurs. Similarly, a pointpotential will be given a reference character corresponding to thereference character of the terminal, juncture or point in the circuit.The vector 67 designates the alternating current input voltage to thebridge 66 which will be in phase with the alternating current voltageapplied to the anodes 6'0. The vectors 71 and 72 lie along the vector67. The juncture 74 between the impedances 71 and 72 is shown as thepoint 74 on the vector diagram of FIGURE 7. The juncture 76 between thecapacitance element 6? and impedance 79 is shown on the vector diagramby the reference character 76. The first arm 75 of the bridge 66 whichincludes the variable resistance 68 and the capacitance element 69 isshown on the vector diagram of FIGURE 7 by the vector 75 Similarly, theimpedance 7% has a vector 76 on the vector diagram. The output voltageof the phase shift bridge 66 that is applied to the grid transformer 7 3is shown by the vector output. The direction of the vector shown on thisvector diagram indicates that the output voltage lags the input voltage67 by an angle approximately degrees. This would permit the rectifiers61 to trigger or fire at a time phase 90 degrees lagging theanode-cathode voltage. The variable resistance 68 may be manuallyadjusted to shift the location of the point 76 to thus adjust the firingangle of the space discharge device 61 and hence adjust the rectifiedoutput to the heating element 52. The temperature responsive impedance71 which is in heat exchange relationship with the heating element 52should have a positive temperature coefficient such that as the heatingelement 52 tends to overheat, the impedance of the temperatureresponsive impedance 71 will increase to decrease the firing angle ofthe rectifier 61 and hence decrease the electrical output to the heatingelement 52. Thus, the phase shift bridge 66 of the control circuit 65maintains a substantially constant temperature of the heating element52.

FIGURE 8 shows a modification of the energization circuit of FIGURE 6.in this case, the rectifier circuit has been shown as a half waverectifier circuit 79 that supplies energy to the heating element 52 of aheating appliance 51 which has again been shown as a flatiron. Atransformer winding 67 again supplies energy to a phase shift bridge 86.This phase shift bridge 34) is shown as having first and secondtemperature responsive impedances 81 and 82 positioned in heat exchangerelationship with the heating element 52. The juncture 83 between theimpedances 81 and 82 is connected to one line 84 of the rectifiercircuit 79. The connection between this juncture 63 and the line 64 hasbeen shown as being made within the flatiron 51 in order that only fourwires need be connected to the flatiron 51. The phase shift bridge 30has first and second arms 85 and 86 with a juncture 8'7 therebetween.The output of the bridge 80 is between the junctures 83 and 87 andapplied to the cathode and grid of the rectifier of the rectifiercircuit 79. The first temperature responsive impedance 81 preferably hasa positive temperature coefiicient and the second temperature responsiveimpedance 82, a negative temperature coefiicient. By so providingpositive and negative temperature coefficients the bridge 80 will beapproximately twice as sensitive as the bridge as of the circuit ofFIGURE 6. It will be obvious that the first temperature responsiveimpedance may have any given temperature coeflicient and the circuitwill operate properly if the second temperature responsive impedance 82has a temperature coeificient that is more negative or less positivethan said iven temperature coeificient.

The vector diagram for the circuit of FIGURE 8 will be essentially thesame as the vector diagram of FIGURE 7 except that there will be twotemperature responsive impedances that vary with temperature changesrather than only one.

The circuit of FIGURE 9 shows a still further modification of acontrollable energization circuit 90 having a half wave rectifiercircuit 91. -In this case, the heating element 52 is again supplied withenergy from the rectifier circuit 91, but the heating element 52 is notin the household appliance which has been shown as a cordless fiatiron92. The heating element is mounted within a container 93. The container93 may be considered as a hot plate for heating the appliance orfiatiron 92 and maintaining same at a substantially constant temperatureas long as this fiatiron 92 is in contact with the hot plate surface 94of the container 93. The arrangement shown in the circuit of FIGURE 9may well be used for cordless automatic fiatirons or as a heatingsurface for any type of appliance such as a hot plate, oven or grill ofa stove. The controllable energization circuit 90 includes a phase shiftbridge 95 having four arms 96, 97, 98, and 99, all of which have beenshown as being in heat exchange relationship with the heating element 52within the container 93. In order to make this phase shift bridge 95 assensitive as possible, the impedances of the first and fourth arms 96and 99 should have a positive temperature coefficient, and theimpedances of the second and third arms 97 and 91; should have anegative temperature coefficient. The vector diagram for the circuit ofFIGURE 9 will be essentially the same as the vector diagram shown inFIGURE 7 except that all four impedances of the bridge are temperatureresponsive in order to make the bridge 95 approximately four times assensitive as the bridge 66 of the circuit of FIGURE 6. The arm 98 isshown as having a variable condenser 190 therein to permit manualadjustment of the operating temperature of the heating element 52.Obviously, a variable resistor may be utilized for this purpose as incircuits described above; however, the variable condenser may haveadvantages of not being affected by the heat produced in the container93 since it will have no movable contact surfaces as is the usual casewith variable resistors. Further, the variable condenser may have atemperature coefficient other than zero, and a negative temperaturecoeificient would still further increase the sensitivity of the bridge95.

The circuit of FIGURE also shows a controllable energization circuit 102having a rectifier 103 for supplying rectified alternating currentenergy to the heating element 52. A household appliance 194 has beenshown as a cooking vessel adapted to be placed in heat exchangerelationship with the heating element 52 as by placing this cookingvessel 1074 on a heating surface 105 of a container 106 which containsthe heating element 52. The cooking vessel 104 has been shown as havinga control impedance 107 incorporated into this cooking vessel 104 whichcontrol impedance 107 is one arm of a phase shift bridge 108. The bridge108 controls the firing angle of the rectifier 1 113. The controlimpedance 107 has a temperature coefiicient other than zero in order tocontrol the output of the phase shift bridge 108 and, hence, control theoutput of the rectifier 103. In the circuit as shown, the controlimpedance 107 should have a negative temperature coefiicient. Thecontrol impedance may take many forms and preferably is a metallic filmimpedance such as shown in the FIGURES l-5. Metallic film impedance havebeen developed which may have the temperature coefiicient thereofcontrolled to a very high degree, and thus a metallic film impedancehaving a very large positive or negative temperature coefiicient may beselected for use as the, control impedance 1117. Such a metallic filmimpedance may be incorporated into the household appliance 104 in amanner similar to that shown in FIGURES 1 and 2 or the method shown inFIGURES 3, 4, and 5. Electrical connections to such metallic filmimpedance may be easily effected and these connections and the metallicfilm impedance themselves could be made water-tight and to present asmooth surface so that the household appliance 104 may easily be washedand kept in a sanitary condition.

The circuit of FIGURE 11 shows a still further energization circuit 111wherein a controllable rectifier 112 supplies rectified alternatingcurrent energy to a heating element 52. The rectifier 112 is controlledby a control circuit 113 which includes a fixed phase shift supplied bythe resistance 114 and the capacitance 115. The resistance 114 has beenshown as being variable to vary the output of the rectifier 112. Athermocouple 116 has been shown as being in heat exchange relationshipwith the heating element 52, and the output of this thermocouple 116 issupplied to an amplifier 117 which amp-lifies the voltage obtained fromthe thermocouple 116- and applies it to the rectifier 112. Thecontrollable rectifier 112 is controlled by a system known as a DC.bias-AC. rider system wherein the resistance and capacitance 114 andsupply a fixed phase shift of approximately ninety degrees lagging theanode voltage and the amplified voltage from the thermocouple supplies avariable direct current for varying the firing angle of the rectifier112. The thermocouple 116 has been shown as being mounted within theheating appliance in close proximity to the heating element 52 so thatit is in heat exchange relationship with this heating element 52. Itwill be obvious that this thermocouple 116 may be mounted in a separateunit such as the arrangement shown in FIG- URE 10.

The circuit of FIGURE 12 shows a still further controllable energizationcircuit 119 for supplying rectified alternating current energy to aheating element 120. The heating element 120 has an intermediateterminal 121, and the right-hand portion 122 of the heating element 12%)serves the dual function of a portion of the heating element and also asone arm of a phase shift bridge 123. The controllable energizationcircuit 119 includes a rectifier device 124 for supplying the rectifiedcurrent to the heating element 120 and this rectified alternatingcurrent is preferably filtered by a filter .125 so as to applyessentially pure direct current to the heating element 120. The phaseshift bridge 123 has condensers 126 and 127 in two arms 128 and of thisbridge 123 to prevent the direct current from flowing in this bridge123. The alternating current impedance of the right-hand portion 122will then be that used as one arm of the bridge 123.

The vector diagram of FIGURE 13 shows the 'vectors obtainable from thecircuit of FIGURE 12. The first arm 12? of the bridge 123 is shown bythe vector 128, likewise the second and third arms 129 and 130 are shownby the vectors 129 and 130. The input voltage to the phase shift bridge123 is shown by the vector input,

and the output voltage of the bridge 123 is shown by the vector output.The right-hand portion 122 of the heating element 121} should beresponsive to temperature changes and, in the circuit as shown, shouldhave a positive temperature coefficient to make a stable circuit. Thesecond arm 129 has been shown as being variable in order to adjust theoutput of the rectifier 124 and hence the temperature of the heatingelement 120.

The heating element 125 may be constructed of a metallic film impedancewith an intermediate terminal connected thereto in order to supply anelectrical connection as at the intermediate terminal 121.

The circuit of FTGURE 14 shows an improvement over the circuit of FIGURE12 wherein only two leads are required to the heating element 131. Theheating element 131 is again supplied with rectified alternating currentenergy from a rectifier 132 as filtered by a filter 133. The heatingelement 131 has been shown as being inductive which will not impede theflow of the direct current from the rectifier 132; however, it willimpede the flow of alternating current applied to it from a phase shiftbridge 134. This phase shift bridge 134 includes first, second, andthird arms 135, 136, and 137, and the heating element 131 constitutesthe fourth arm of this bridge 134.

The vector diagram of FIGURE shows the vectors obtainable from thebridge 134 wherein the arm 131 may have a high alternating currentimpedance relative to the first and second arms 135 and 136, and hencethis bridge 134 may be made quite sensitive. An advantage of the circuitof FIGURE 14 is that the heating element 131 performs the dual functionof heating and control of the rectifier 132. No intermediate terminalsare needed and hence merely the two end terminals of the heating element131 need exist. The heating element 131 would thus be desirable for aportable heating appliance such as a flatiron which may then have merelythe two normal wires for electrical connection to such heating elementand need not have an extra wires or any separate control impedance.

FIGURE 16 is a further modification of the invention wherein a heatingelement 152 is supplied with rectified alternating current energy fromthe rectifier 153. The heating element 152 is adapted to be mounted in abase unit 154 which may have ears 155 as an aid in centering theflatiron 156 on the base unit 154-. The flatiron 156 has a controlimpedance 157 contained therein and adapted to be in heat exchangerelationship with the heating element 152 when the flatiron 156 isplaced on a heating surface 158 on the base unit 154. The rectifier 153has a bridge circuit 159 for control of the rectifier 153 and thecontrol impedance 157 is adapted to be placed in parallel with one arm160 of the bridge circuit 159. The electrical connection between thecontrol impedance 157 and the bridge circuit 159 is provided by terminalplates 161 in the flatiron 156 and terminal plates 162 in the base unit154. The terminal plates 161 are electrical insulated from the flatiron156 by insulators 163 and the terminal plates 162 are insulated from thebase unit 154 by insulators 164. The terminal plates 161 and 162 maymake electrical connection by surface contact or preferably by a plugand jack connection 165 and 166.

When the flatiron is placed upon the heating surface 158 so that theterminal plates 161 and 162 are in electrical contact, then the controlimpedance 157 is in parallel with the arm 169 to reduce the totalimpedance in this arm of the bridge circuit 159. This is arranged tocause the phase of the grid-cathode voltage to lag to a greater degreethe phase of the anode-cathode voltage of the rectifier 153. This willreduce the electrical output of the rectifier 153 and reduce the heatproduced by the heating element 152. A fourth arm 169 of the bridge 159is made adjustable to provide for the manual variation of the operationtemperature of the fiatiron 156. This will be the case when the flatiron156 is in heat exchange relationship with the eating element 152 and thecontrol impedance 157 is part of the bridge circuit 159. When thefiatiron 156 is removed from the base unit 154, the control impedance157 will no longer be in parallel with the arm 161} and, hence, theimpedance of such arm will increase to increase the electrical output ofthe rectifier 153. The heating element 152 will then raise intemperature in accordance with the increased electrical input thereto.When the fiatiron 156 is again placed on the base unit 152, the controlimpedance 157 will be in shunt with the arm to reduce the output of therectifier 153 to a value which will produce the desired temperaturesetting as dictated by the variable arm 167. However, the stored heat inthe base unit 152 will rapidly raise the temperature of the fiatiron 156to this operating temperature. The control impedance 157 shouldpreferably be of a negative temperature coeflicient so that it will havea regulating effect upon the operation of the bridge circuit 159 andrectifier 153. Sec- 0nd and third arms 167 and 168 of the bridge 159 mayhave a positive temperature coefiicient to control the bridge 159 whenthe flatiron 156 is removed from the base unit 154 and hence control thetemperature of the base unit 152, and in such case the arms 167 andshould be in heat exchange relationship with the base unit 152.

The FIGURE 17 shows the vector diagram for the circuit of FIGURE 16wherein 161i is the voltage vector for the arm 166 and output is theoutput voltage of the bridge circuit 159. When the control impedance 157is not in shunt with the arm 16%, the impedance of the arm 160 willincrease to that shown by the dotted line vector 16!) and the outputvoltage will shift to a position less lagging with respect to the inputvoltage.

Any of the temperature responsive elements 71, 81, 82, 96, 1 7, 9%, 99,116, 122, 131, 157, 167, and 168, just as the sensing element 1197 maybe in the form of a metallic impedance film, and constructed similarlyto that shown in FIGURES 1 to 5, either as an individual film or incombination with a separate film as the heating element.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. A control system for a household appliance such as a flatironcomprising, a base unit, said appliance adapted to rest on said baseunit to be heated, ears on said base unit to centrally locate saidflatiron on said base, a temperature sensing device having changeableconditions with varying temperatures located in said appliance for heatexchange relationship therewith, a heater resistance in said base unit,means for connecting said heater resistance to an alternating currentsource for energizing said resistance, and control means including saidsensing device whereby said sensing device controls the current to saidheater resistance and hence the resultant temperature of said base unitand appliance.

2. An electronic tube control for a household heating appliance,comprising, a base unit, said heating appliance adapted to rest on saidbase unit to be heated, a temperature sensing element located in saidappliance for heat exchange relationship with said base unit, a heaterresistance in said base unit, a controllable rectifier having an inputand an output and control means, means for connecting said input to analternating current source for energizing said rectifier, means forconnecting said output to said heater resistance for passing rectifiedcurrent therethrough, a phase shift bridge circuit having four arms andan input and an output, means for including said sensing element in anarm of said bridge, means for connecting said bridge input to saidalternating current source for energizing same, means for connectingsaid bridge output to said rectifier control means, whereby said sensingelement controls the rectified current to said heater resistance andhence the resultant temperature of said base unit and applicance.

3. An electronic tube control for a household heating applicance,comprising, a base unit, said heating appliance adapted to rest on saidbase unit to be heated, a temperature sensing element located in saidappliance for heat exchange relationship with said base unit, first andsecond electrical connections to said sensing element, third and fourthelectrical connections in said base unit to make electrical connectionto said first and second connections when said appliance is resting onsaid base unit, a heater resistance in said base unit, a controllablerectifier having an input and an output and control means, means forconnecting said input to an alternating current source for energizingsaid rectifier, means for connecting said output to said heaterresistance for passing rectified current therethrough, a phase shiftcircuit having an input and an output, means for connecting said circuitinput to said alternating current source for energizing same, means forconnecting said circuit output to said rectifier control means forvariably controlling the rectified output of said rectifier, and meansfor connecting on arm of said circuit arm to said third and fourthconnections to place said sensing element in parallel with said arm whensaid appliance is resting on said base unit, whereby said sensingelement when connected in parallel to said arm controls the rectifiedcurrent to said heater resistance and hence the resultant temperature ofsaid base unit and appliance, and whereby the circuit establishes agreater amount of rectified current to said heater resistance and hencea greater resultant temperature of said base unit when said appliance isremoved from said base unit.

4. An electronic tube control for a household fiatiron, comprising, abase unit, said fiatiron having a soleplate adapted to rest on said baseunit to be heated, ears on said base unit to centrally locatet saidflatiron on said base, a temperature sensing element having anappreciable negative temperature coeflicient of impedance located insaid fiatiron in heat exchange relationship with said soleplate, firstand second electrical plug connections in the toe and heel,respectively, of said soleplate and connected to opposite ends of saidsensing element, first and second electrical jack connections in saidbase unit to make electrical connection to said plug connections whensaid soleplate is resting on said base unit, a heater resistance in saidbase unit in heat exchange relationship with said soleplate when saidsoleplate is resting on said base unit, a gaseous c011- trollablerectifier having an input and an output and control means, means forconnecting said input to an alternating current source for energizingsaid rectifier, means for connecting said output to said heaterresistance for pass ing rectified current therethrough, a phase shiftbridge circuit having four arms and an input and an output, means forconnecting said bridge input to said alternating current source forenergizing same, means for connecting said bridge output to saidrectifier control means for variably controlling the rectified output ofsaid rectifier, a first of said arms being capacitive, means forconnecting said first arm to said first and second jack connections toplace said sensing element in parallel with said first arm when saidsoleplate is resting on said base unit, a second arm of said bridgeopposite said first arm being manually variable in impedance to changethe phase of the bridge output voltage, and the third and fourthopposite arms of said bridge each having an appreciable positivetemperature coefficient of impedance and being in heat exchangerelationship with said heater resistance whereby said sensing elementwhen connected in parallel to said first arm controls the rectifiedcurrent to said heater resistance and hence the resultant temperature ofsaid base unit and fiatiron, and whereby the bridge establishes agreater amount of rectified current to said heater resistance and hencea greater resultant temperature of said base unit when said fiatiron isremoved from said base unit.

References Cited in the file of this patent UNITED STATES PATENTS287,758 Dyer et a1 Oct. 30, 1883 925,050 Sprenger June 15, 19091,664,758 Reynolds Apr. 3, 1928 1,694,264 Hull Dec. 4, 1928 2,083,382Jutson et a]. June 8, 1937 2,086,966 Shrader July 13, 1937 2,673,917Woodling Mar. 30, 1954 3,007,026 Woodling Oct. 31, 1961

1. A CONTROL SYSTEM FOR A HOUSEHOLD APPLIANCE SUCH AS A FLATIRONCOMPRISING, A BASE UNIT, SAID APPLIANCE ADAPTED TO REST ON SAID BASEUNIT TO BE HEATED, EARS ON SAID BASE UNIT TO CENTRALLY LOCATE SAIDFLATIRON ON SAID BASE, A TEMPERATURE SENSING DEVICE HAVING CHANGEABLECONDITIONS WITH VARYING TEMPERATURES LOCATED IN SAID APPLIANCE FOR HEATEXCHANGE RELATIONSHIP THEREWITH, A HEATER RESISTANCE IN SAID BASE UNIT,MEANS FOR CONNECTING SAID HEATER RESISTANCE TO AN ALTERNATING CURRENTSOURCE FOR ENERGIZING SAID RESISTANCE,